This invention relates to a magnetron and more particularly to a magnetron having a longitudinal type cooling structure.
Magnetrons used in microwave ovens are generally provided with cooling fins. The cooling fins are secured around a cylindrical anode wall within the magnetron for cooling by forced air flow. The cooling fins of the prior art have either a longitudinal type structure or a lateral type structure. The lateral cooling structure comprises fins which are fitted radially around the anode wall to form air flow paths transverse to the axis of the anode. The longitudinal cooling structure comprises fins which are also fitted radially around the anode wall, however, air flow paths are created along the anode axis rather than transverse thereto. One conventional magnetron (i.e., external magnet type magnetron), utilizing either a longitudinal or lateral type cooling structure, has an antenna output portion disposed coaxially with the anode axis. The cooling fins of this coaxial structure are of equal length. Such a concentric antenna structure permits the magnetron to be adapted to almost all types of ovens. That is, the concentricity of such a magnetron upon being rotated on its antenna terminal axis to its mounting position on the waveguide within the oven facilitates accessiblity to the magnetron's input plug and alignment with the pre-positioned air flow duct within the oven.
In recent years, however, an internal magnet type magnetron has been developed; this magnetron has a smaller size and lighter weight than the previously used magnetrons. Because of its size and weight internal magnet type magnetrons are generally used. The simplest internal magnet magnetron to manufacture is the type wherein the antenna terminal is offset from the anode axis. The offset is created by the necessary positioning of a permanent magnet along the anode axis adjacent the antenna output terminal. Consequently, the antenna terminal must be positioned away from the anode axis (i.e., offset) to permit the antenna lead to reach the antenna terminal. As with all magnetrons, the internal magnet magnetron also comprises cooling fins of equal length which are fitted radially around the anode wall, wherein the periphery of these fins from the overall shape of the magnetron.
In view of the fact the antenna terminal is offset from the anode axis and the fins are of equal length, each point on the periphery of the fin does not lie at a substantially uniform distance from the antenna axis. Consequently, upon rotating the prior art internal magnet magnetron on its antenna terminal axis during mounting to the waveguide eccentricity will be experienced.
Several disadvantages result from mounting an offset antenna terminal of the internal magnet magnetron and its concomitant eccentricity to a microwave oven. First, it is necessary for the magnetron to be adaptable to substantially all types of oven waveguides. The eccentricity caused by the offset and equal length fins makes aligning the magnetron mounting bracket with the standard waveguide mounting holes of various ovens very difficult. Second, the mounting space for the magnetron within standard microwave ovens is very limited. The eccentricity caused by the offset and equal length fins produces misalignment of its coolant guiding means, surrounding the fins of the magnetron, with the pre-positioned air flow duct within the oven. Third, because of the limited space within the oven and the eccentricity experienced by these prior art magnetrons during mounting, frequent inaccessibility to the magnetron's input plug occurs.